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| United States Patent |
5,125,811
|
|
Amano
, et al.
|
June 30, 1992
|
Sintered iron-base alloy vane for compressors
Abstract
A compressor vane of a sintered iron-base alloy composed of an iron-base
matrix containing hard carbides uniformly dispersed therein, characterized
in that the sintered iron-base alloy consists essentially of 0.7 to 1.5%
by weight C, 3.0 to 5.0% by weight Cr, 0 to 10.0% by weight Mo, 1 to 20.0%
by weight W, 0.5 to 6.0% by weight V, 0 to 15.0% by weight Co and the
balance iron and inevitable impurities, and that the compressor vane is
produced by molding under a pressure of 5 to 8 ton/cm.sup.2 and then
sintering at a temperature of less than 1250.degree. C. so as to control
particle size of the hard carbide to not more than 5 .mu.m, as well as to
control the theoretical relative density to 80 to 90%, and to control the
macro-hardness to 10 to 45 in the Rockwell C scale.
| Inventors:
|
Amano; Nobuya (Itami, JP);
Motooka; Naoki (Itami, JP)
|
| Assignee:
|
Sumitomo Electric Industries, Ltd. (Osaka, JP)
|
| Appl. No.:
|
623660 |
| Filed:
|
December 28, 1990 |
| PCT Filed:
|
April 27, 1990
|
| PCT NO:
|
PCT/JP90/00561
|
| 371 Date:
|
December 28, 1990
|
| 102(e) Date:
|
December 28, 1990
|
Foreign Application Priority Data
| Current U.S. Class: |
418/179; 29/888.025; 29/889.7; 419/38 |
| Intern'l Class: |
F03C 002/00 |
| Field of Search: |
29/889.7,888.025
418/179
419/23,38
|
References Cited
U.S. Patent Documents
| 4490175 | Dec., 1984 | Matsuzaki | 418/179.
|
| 4772450 | Sep., 1988 | Friedman | 29/889.
|
| 4817858 | Apr., 1989 | Verpoort | 29/899.
|
| 4859164 | Aug., 1989 | Shimomura | 418/179.
|
Primary Examiner: Cuda; Irene
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
We claim:
1. A compressor vane of a sintered iron-base alloy composed of an iron-base
matrix containing hard carbides uniformly dispersed therein, characterized
in that said sintered iron-base alloy consists essentially of 0.7 to 1.5%
by weight C, 3.0 to 5.0% by weight Cr, 0 to 10.0% by weight Mo, 1 to 20.0%
by weight W, 0.5 to 6.0% by weight V, 0 to 15.0% by weight Co and the
balance iron and inevitable impurities, said compressor vane of a sintered
iron-base alloy being produced by molding under a pressure of 5 to 8
ton/cm.sup.2 and then sintering at a temperature of less than 1250.degree.
C. so as to control particle size of the hard carbide to not more than 5
.mu.m, as well as to control the theoretical relative density to 80 to
90%, and to control the macro-hardness to 10 to 45 in the Rockwell C
scale.
2. A compressor vane of a sintered iron-base alloy according to claim 1
wherein said matrix contains 0.3 to 3 wt % of at least one solid lubricant
selected from the group consisting of CaF.sub.2, BaF.sub.2, MoS.sub.2 and
WS.sub.2.
Description
TECHNICAL FIELD
The present invention relates to a compressor vane and, more particularly,
a sintered iron-base alloy vane for a compressor required to have wear
resistant properties.
BACKGROUND ART
In general, as a material for fluid-pressurizing vanes which are sliding
parts of compressors, there have generally been used special cast irons,
and high-carbon or high speed tool steels with excellent wear resistance.
Also, carbon vanes are sometimes used for heavy-load compressors.
However, with development of compressors with higher performance and larger
load-carrying capacity, it has been found that the special cast-iron vanes
involve such a problem that they are poor in wear resistance. On the other
hand, the high-carbon or high speed tool steel vanes possess excellent
wear resistance as their hardness may be improved by thermal treatments,
but they attack opposing parts and cause seizure because of their poor
self-lubricating ability. Also, the carbon vanes have such a problem that
they are too expensive.
Recently, sintered alloy vanes produced by sintering have partially
received practical application. Such sintered alloy vane are composed, as
disclosed in the Japanese Patent Gazette of laying-open No. 59-16952 for
example, of a sintered iron-base alloy consisting of a matrix of a base
metal of iron and hard particles such as carbides dispersed in the matrix.
In such vanes, the mechanical strength of the matrix is ensured by
increasing the theoretical relative density to not less than 92%, while
the wear resistance is improved by dispersion of the hard particles with a
diameter of not less than 5 .mu.m into the matrix. Also, such sintered
alloy vanes have a further advantage such that they possess
self-lubricating when oil is impregnated into their pores.
However, the above sintered iron-base alloy vanes attack opposing parts and
cause a seizure in a manner similar to the aforesaid steel vanes because
of their high hardness of a macro-structure including the dispersed hard
particles, which results from high theoretical relative density of not
less than 92%.
DISCLOSURE OF INVENTION
The present invention has been made under such situations of the prior art
to provide a sintered iron-base alloy vane, which possesses high wear
resistance but does not damage opposing parts, for use in compressors
which are advancing increase in performance and in load-carrying capacity.
According to the present invention, the above and other objects are
achieved by molding a sintered iron-base alloy, which is composed of a
matrix of a base metal of iron and containing hard carbides uniformly
dispersed therein, and which consists essentially of 0.7 to 1.5% by weight
C, 3.0 to 5.0% by weight Cr, 0 to 10.0% by weight Mo, 1 to 20.0% by weight
W, 0.5 to 6.0% by weight V, 0 to 15.0% by weight Co and the balance iron
and inevitable impurities, under a pressure of 5 to 8 ton/cm.sup.2, and
then sintering compacts at a temperature of less than 1250.degree. C. so
as to control particle size of the hard carbide to not more than 5 .mu.m,
as well as to control the theoretical relative density to 80 to 90%, and
to control the macro-hardness to 10 to 45 in the Rockwell C scale.
The sintered iron-base alloy used for compressor vanes of the present
invention is not limited in its composition, and may be the one
conventionally used as a sintered material for sintered iron-base vanes,
or the one having any composition composed of a base metal of iron and
containing a hard carbide uniformly dispersed therein. It is, however,
preferred to use a sintered iron-base alloy having a composition
consisting essentially of 0.7 to 1.5 wt % C, 3.0 to 5.0 wt % Cr, 0 to 10.0
wt % Mo, 1 to 20.0 wt % W, 0.5 to 6.0 wt % V, 0 to 15.0 wt % Co, and the
balance iron and inevitable impurities.
The hard carbide may be the one conventionally used in sintered iron-base
alloy vanes. For example, there may be used those such as carbides of Cr,
Mo, V, W and the like. It is, however, preferred to use carbides with a
particle size of not more than 5 .mu.m.
The above sintered iron-base alloy may further contain 0.5 to 3% by weight
of at least one solid lubricant selected from the group consisting of
CaF.sub.2, BaF.sub.2, MoS.sub.2 and WS.sub.2 as occasion demands, which is
incorporated into the alloy to improve its self-lubricating ability.
The sintered iron-base alloy vanes are produced by powder metallurgy, but
it is required to produce the same by molding powdered raw materials into
compacts in the form of vanes under a pressure of 5 to 8 ton/cm.sup.2, and
then sintering the compacts at a temperature of less than 1250.degree. C.,
preferably, at a temperature ranging from 1000.degree. to 1200.degree. C.
to achieve the object of the present invention. In general, the resultant
sintered bodies are treated before use by hardening and tempering to
improve its wear resistance.
The sintered iron-base alloy for vanes of the present invention are
sintered under the above conditions to control the particle size of hard
carbides dispersed in the matrix to not more than 5 .mu.m, as well as to
control the theoretical relative density to 80 to 90% and to control the
macro-hardness to 10 to 45 in the Rockwell C scale. Thus, the sintered
iron-base alloy vanes possess excellent self-lubricating and
sliding-movement properties and don't cause damage such as part seizures
as they are lowered in aggression to the opposing parts.
The reasons why the production conditions, particle size of the hard
carbide in the matrix, theoretical relative density, and macro-hardness of
the sintered alloy vanes of the present invention have been limited as
above are as follows.
The molding pressure of powder of raw materials has been limited to 5 to 8
ton/cm.sup.2 for the following reasons: If the molding pressure is less
than 5 ton/cm.sup.2, the relative density after sintering becomes less
than 80%, thus making it impossible to obtain sufficient mechanical
strength and wear resistance required for vanes. If the molding pressure
is more than 8 ton/cm.sup.2, there is a possibility of the relative
density exceeding 90%, so that the aggression to the opposing parts
increases.
If the sintering temperature is not less than 1250.degree. C., the particle
size of the carbide exceeds 5 .mu.m because of increase of the generation
of a liquid phase during sintering, which causes increase in the grain
size of the carbide.
The reasons why the particle size of the hard particles in the matrix has
been limited to not more than 5 .mu.m are as follows. If the particle size
exceeds 5 .mu.m, the aggression to the opposing parts increases.
If the theoretical relative density is less than 80%, the vanes are
insufficient in the strength and lack the wear resistance because of
lowering of the hardness. If the theoretical density exceeds 90%, the
hardness becomes considerably increased, thus making it difficult to
control the macro-hardness to a value within the scope of the present
invention even if the products are subjected to the thermal treatments
such as annealing in the subsequent steps. As a result, the aggression to
the opposing parts becomes a problem.
Further, the reasons why the hardness of the macro structure has been
limited to 10 to 45 in the Rockwell C scale are as follows. If the
macro-hardness is less then 10, the wear resistance of the vanes becomes
insufficient. If the macro-hardness exceeds 45, the aggression to the
opposing parts becomes considerably increased.
The reasons why the amount of the solid lubricant to be incorporated into
the alloy to improve the self-lubricating ability has been limited to 0.5
to 3 wt % are as follows: If the added amount of the solid lubricant is
less than 0.5 wt %, the self-lubricating property is scarcely obtained. If
the added amount of the solid lubricant exceeds 3 wt %, the quality of the
compacted body before sintering becomes lowered and the expansion tend to
be taken place during sintering take place. Also, the deflective strength
of the vanes becomes considerably lowered.
According to the present invention, it is possible to provide sintered
iron-base alloy vanes for use in compressors with increasing performance
and load-carrying capacity, which possess high wear resistance and retain
stable sliding-movement properties for a long period of time without
causing damage of the opposing parts.
Accordingly, it is possible to considerably cut down the manufacturing cost
of heavy-load compressors by using the sintered iron-base alloy vanes of
the present invention instead of the expensive carbon vanes.
BEST MODE FOR CARRYING OUT THE INVENTION
EXAMPLE 1
Alloy powder, a minus sieve of a 100 mesh screen, consisting of, 1.1% by
weight C, 6.1% by weight W, 5.0% by weight Mo, 4.0% by weight Cr, 2.0% by
weight V and the valance iron and inevitable impurities was mixed with
0.8% by weight of zinc stearate serving as a molding auxiliary, and then
molded in the form of compressor vanes under a pressure ranging from 4 to
8 ton/cm.sup.2. The compacted bodies were sintered in vacuum at a
temperature of 1180.degree. to 1250.degree. C. for 1 hour, and then
treated by gas-hardening in N.sub.2 gas from 1150.degree. C. and tempering
twice at 500.degree. to 650.degree. C. to provide sintered iron-base alloy
vanes as specimens 1-1 to 1-12.
For each of the resultant vanes, measurements were made on theoretical
relative density, macro-hardness (Rockwell C scale) and particle size of
carbides. Separate from the above, each vane was assembled into a
compressor to perform durability tests for 500 and 1500 hours. In this
case, a piston, i.e., an opposing part, of the compressor is of Mo-Ni-Cr
cast iron and a cylinder is of cast iron. The results are shown in Table
1.
As will be understood from Table 1, specimens 1-3 to 1-10 according to the
present invention possess excellent wear resistance, whereas specimens 1-1
and 1-2 which are low in the theoretical relative density and in
macro-hardness possess large wear. The specimens 1-11 and 1-12, which are
large in particle size of the carbide and high in theoretical relative
density and in high macro-hardness, aggress the opposing parts heavily,
resulting in considerable wear of the opposing parts.
TABLE 1
__________________________________________________________________________
Molding Sintering
Tempering
Particle
Relative
Macro-
Pressure temp.
temp. size of
Density
Hardness
Durability Test
Specimen
(ton/cm.sup.2)
(.degree.C.)
(.degree.C.)
carbide (.mu.m)
(%) (H.sub.R C)
500 hrs
1500 hrs
__________________________________________________________________________
1-1 4 1180 650 3-5 78 5-8 Wear:
Wear:
large
large
1-2 " " 640 " " 6-11
good
Wear:
large
1-3 5 " " 2-5 80 10-15
" good
1-4 " " 620 3-5 " 15-20
" "
1-5 6 " " " 83 13-18
" "
1-6 " " 600 2-5 " 18-23
" "
1-7 7 " 580 2-4 85 27-32
" "
1-8 " " 560 3-5 " 29-35
" "
1-9 8 " 540 2-3 90 35-40
" "
1-10 " " 520 2-4 " 38-44
" "
1-11 " 1250 " 6-10 92 45-49
" Wear of op-
posing part:
large
1-12 " " 500 7-10 " 50-55
" Wear of op-
posing part:
large
__________________________________________________________________________
EXAMPLE 2
Alloy powder, a minus sieve of a 100 mesh screen, consisting essentially of
1.5% by weight C, 12% by weight W, 0.3% by weight Mo, 4.0% by weight Cr,
4.5% by weight V and the valance iron and inevitable impurities, was added
with 0 to 5% by weight of a solid lubricant and 0.8% by weight of the
molding auxiliary. The resultant mixture was molded into compacts in the
form of a plate with 30.times.20.times.5 mm under a pressure of 6
ton/cm.sup.2. The compacts were sintered in vacuum at 1180 .degree. C. for
1 hour, gas-hardened with N.sub.2 gas from 1150.degree. C., and then
tempered twice at 580 .degree. C. to prepare specimens.
For each of the resultant specimens 2-1 to 2-10, measurements were made on
the theoretical relative density, macro-hardness (Rockwell C scale),
particle size of carbide in a manner similar to that of Example 1. Also,
for each specimen, wear resistance test was carried out, using the
specimen as a fixed member and a Meehanite cast iron plate of a 30 mm
outer diameter.times.16 mm inner diameter.times.3 mm height as a rotating
member (Test conditions: Velocity of rotating member: 5 m/sec, Time: 10
hours, no lubricant), to determine the maximum depth of wear formed in the
specimen which is the fixed member. The results are summarized in Table 2.
TABLE 2
__________________________________________________________________________
Solid lubricant Particle
Relative
Macro-
Depth
Deflective
Added Amount
size of
Density
Hardness
of Wear
Strength
Specimen
Kind (% by weight)
carbide (.mu.m)
(%) (H.sub.R C)
(mm) (kg)
__________________________________________________________________________
2-1 -- 0 3-5 83 13-18
0.32 3650
2-2 CaF.sub.2
0.2 3-4 " 14-19
0.34 3500
2-3 MoS.sub.2
0.5 3-5 " 13-16
0.28 3450
2-4 CaF.sub.2
1 3-4 " 15-20
0.24 3300
2-5 MoS.sub.2
1 3-5 82 14-16
0.22 3350
2-6 CaF.sub.2
3 2-4 " 15-18
0.18 3200
2-7 MoS.sub.2
3 2-5 " " 0.20 3050
2-8 CaF.sub.2 + MoS.sub.2
3 2-4 81 13-15
" 3100
2-9 CaF.sub.2
5 2-5 80 11-14
0.19 2650
2-10 CaF.sub.2 + MoS.sub.2
5 2-5 " 10-13
0.20 2600
__________________________________________________________________________
As will be understood from Table 2, the specimens with the content of the
solid lubricant being 0.2% by weight possess a wear depth same as that of
the specimen containing no lubricant. In contrast therewith, it was
observed that the lubricant added in an amount of not less than 0.5% by
weight causes reduction in the wear depth because of improvement in the
self-lubricating properties. However, the deflective strength was
considerably lowered when the content of the lubricant is incorporated in
an amount of more than 3% by weight.
EXAMPLE 3
Alloy power, a minus sieve of a 100 mesh screen, consisting essentially of
1.5 wt % C, 1.0 wt % Mo, 12 wt % Cr, 0.5 wt % V and the valance iron and
inevitable impurities, was mixed with 0.8 wt % of the molding auxiliary,
and then compacted to provide cylinders with 15 mm in diameter.times.20 mm
in length under a pressure of 7 ton/cm.sup.2. The compacts were sintered
in vacuum at 1180.degree. to 1250.degree. C. for 1 hour, then gas-hardened
in N.sub.2 gas from 1150.degree. C., and tempered twice at 580.degree. C.
For each of the resultant specimens 3-1 to 3-6, measurements were made on
the theoretical relative density, macro-hardness (Rockwell C scale, and
particle size of carbides in a manner similar to Example 1. Also, using
each specimen as a fixed member, and a Meehanite cast iron ring of 20 mm
(outer diameter).times.12 mm (inner diameter).times.20 mm (length) as a
rotating member, a wear resistance test was carried out for each specimen.
Test conditions are: velocity of a rotating member 7 m/sec, Time: 1 hours,
no lubricant, Load: 40 kg). The width of wear formed on the fixed member,
i.e., specimen, and reduction in diameter of the rotating member were
measured. For comparison, there were prepared comparative specimens 3-7 to
3-10 made of a molten alloy and having the same dimensions that the
specimen have. For each comparative specimen, wear resistance test was
carried out in the same manner mentioned above. The results are shown in
Table 3.
TABLE 3
__________________________________________________________________________
Particle Width of
Reduction
Sintering
Diameter
Relative
Macro-
Wear for
in Diameter
temp. (.degree.C.)
of carbide
Density
Hardness
fixed of rotating
Specimen
Kind or Material
(.mu.m)
(%) (H.sub.R C)
member (mm)
member (mm)
__________________________________________________________________________
3-1 Sintered material
1180 2-4 85 28-33
0.40 0.010
3-2 Sintered material
" " 87 32-40
0.39 0.010
3-3 Sintered material
1200 3-5 88 35-42
0.38 0.015
3-4 Sintered material
" " 90 39-45
0.35 "
3-5 Sintered material
1250 5-8 92 48-52
0.33 0.030
3-6 Sintered material
" 7-10 95 55-60
0.30 0.040
3-7 Molten material
SUJ-2 10-20 100 60-63
0.25 0.050
3-8 Molten material
SKH-9 " " 63-65
0.23 0.055
3-9 Molten material
SKD-11
" " 60-63
0.26 0.050
3-10 Molten material
Special
15-30 " 40-43
0.38 0.030
cast iron
__________________________________________________________________________
As will be understood from Table 3, the specimens 3-5 and 3-6 of a sintered
material, and specimens 3-7 to 3-10 of a molten material are small in wear
because of large particle size of carbide and large macro-hardness, but
the wear of the opposing parts (rotating member) becomes considerably
increased and is two or more times that of the specimen 3-1 to 3-4 of the
present invention.
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